Liquid storage chamber

ABSTRACT

A below ground chamber for the storage of liquid gas at cryogenic temperatures and a method for constructing the same. An outer shell is formed and an inner shell is spaced interior of the outer shell so formed. The space between the two chambers is frozen under a controlled pressure for providing an internal stress in the frozen space. The unfrozen earth central of the frozen space is excavated to form the storage chamber and a roof is constructed over the chamber.

[ 1 Mar. 7, 1972 United States Patent Bodle et al.

[54] LIQUID STORAGE CHAMBER 3,411,302 11/1968 Nachsen................................6l/.5X

[72] Inventors: William W. Bodle, Bannockburn; Phillip J.

Anderson, Deerfield, both of I11.

Institute of Gas Technology May 19, 1969 [21] Appl. No.: 825,687

Primary Examiner.lacob Shapiro Attorney-Molinare, Allegretti, Newitt and Witcoff [57] ABSTRACT A below ground chamber for the storage of liquid gas at [73] Assignee:

[22] Filed:

cryogenic temperatures and a method for constructing the same. An outer shell is formed and an inner shell is spaced interior of the outer shell so formed. The space between the two chambers is frozen under a controlled pressure for providing an internal stress in the frozen space. The unfrozen earth central of the frozen space is excavated to form the storage QJMS M/M m a g 6 6 6 3 1 e 6 "A s m m .5. .1 m

[52] US. [51] Int. Cl...... [58] Field chamber and a roof is constructed over the chamber.

10 Claims, 3 Drawing Figures References Cited UNITED STATES PATENTS mourn STORAGE CHAMBER BACKGROUND OF THE INVENTION Field of the Invention and Description of the Prior Art This invention relates to a belowground chamber for the storage of liquid gas at cryogenic temperatures and to a method for forming the same, and it particularly relates to such a chamber which has a bottom and sides formed by frozen earth materials, including rock and soil.

Gas utility companies which supply natural gas for heating, cooking, and the like encounter problems on extremely cold days of the year when the heating demand is high and extremely large quantities of heating gas are required. On these high-demand days, the gas supplied through pipelines extending from distant gas storage chambers are inadequate to supply the gas required by the utility companys customers. As a result, it has been common for gas utility companies to provide conveniently located storage tanks for gas for use on the peak demand days. It has been customary to provide large aboveground storage tanks where the gas is stored, the gas being maintained in the gaseous state in these aboveground tanks.

The storage of gas in such aboveground tanks has certain disadvantages. First, there is a safety hazard in having a large quantity of gas stored aboveground. If a leak should develop in the tank and the gas became accidentally ignited, injury and damage could result. Secondly, the storage of the gas in the gaseous state requires extremely large volume storage tanks to assure that the company will have sufficient gas to meet its customers demand on the high-demand days.

Because of these problems, gas utility companies, in recent years, have sought to provide for the storage of gas in belowground or partially belowground chambers or tanks, wherein the gas storage is in the liquid state whereby far greater quantities of gas are stored in a chamber of given size, as compared to storage in the gaseous state. Several methods have been used for constructing these belowground or partially belowground chambers or tanks. Basically, the two most common methods involve constructing a storage chamber completely below ground level where access is provided to the chamber by an inclined adit. Secondly, it is also possible to excavate a hole in the ground" having a bottom and sides, and a top or roof is constructed over the excavation.

The use of such belowground systems for the storage of liquid gas at atmospheric pressure and cryogenic temperatures is limited by geological conditions. For example, in an underground storage system, it is economically desirable to have a substantial portion of the chamber formed within a rock or self-supporting earthen formation. If the soil is sandy or marshy, such a self-supporting formation is not possible. Similar problems are encountered in providing a system where the chamber is formed by first digging a hole in the ground. It would be desirable for the soil to be self-supporting when the excavation is made. However, if the hole which is dug is in a sandy or wet area, support structure must be provided, and the cost of the structure is significantly increased. Any structure for making the floor, walls, and roof of a chamber involves undesirable expenses.

To overcome the disadvantages of underground storage chambers, storage facilities have been provided wherein the bottom and walls are formed by first freezing the water in the earth surrounding the bottom and sides of the chamber to be provided, and then excavating the unfrozen space interior of the frozen area. Freeze pipes are placed into the moist soil, refrigerant is pumped into the pipes until a frozen wall of the desired thickness, such as to 30 feet, is provided around these sides and the bottom of the soil which is to be excavated. When a suitable frozen shell has been provided, the unfrozen enclosed soil is excavated, a roof is placed over the excavation, and the cold liquid gas is pumped into the chamber thus formed. Such a system is found to be highly economical because substantially no physical structure is required for forming the walls and floor. Also, the walls and floor are already cold when the liquid gas is pumped therein, so that the walls act as a natural insulating medium and the amount of heat transfer from the exterior to the cold liquid gas is substantially reduced. One problem, however, has been encountered in the storage of liquid gases at cryogenic temperatures when using such storage facilities. The liquid gas has been found to boil off at such a high rate that it becomes uneconomical to Iiquefy enough gas to fill the chamber in a reasonable period of time. It is believed that this problem is caused by cracking of the frozen earth because of the stress applied thereto by the liquid filling the chamber. When cracks are formed, there is a greater amount of heat transfer surface, and because of the greater heat transfer surface, there is more heat transfer to the cold liquid gas and the undesirably high-boiloff rate occurs.

SUMMARY OF THE INVENTION It is therefore an important object of this invention to provide a method and system for the storage of liquid gas at cryogenic temperatures and atmospheric pressures wherein at least the walls and floor of the storage chamber are frozen under a built-in stress so that as the cold liquid fills the chamber, the built-in stresses substantially avoid cracking and thereby increased heat transfer surface exposed to the liquid gas.

It is also an object of this invention to provide an improved underground storage system for liquid gas wherein the system and method are characterized by their simplicity and efficiency in use.

It is further object of this invention to provide an improved method and system for storing liquid gas at cryogenic temperatures and at atmospheric pressure wherein the cracking of the frozen earth formation is substantially reduced.

Further purposes and objects of this invention will appear as this specification proceeds.

The foregoing objects are accomplished by providing a belowground chamber, wherein an outer rigid chamber is formed, an inner rigid chamber spaced from the outer rigid chamber is formed, the earthen formation defined in the space between the outer chamber and the inner chamber is then frozen while the pressure in this intermediate space is maintained at a predetermined level above atmospheric pressure, the earth in the unfrozen space interior of the intermediate space is excavated to define the gas storage chamber, and a roof is constructed over the thus excavated chamber.

BRIEF DESCRIPTION OF THE DRAWINGS A particular embodiment of the present invention is illustrated in the accompanying drawings wherein:

FIG. 1 is a schematic vertical cross-sectional view showing the first step in our process for forming an improved below ground chamber for the storage of liquid gases;

FIG. 2 is a view similar to FIG. 1 except showing the second step of the process for forming our improved underground storage chamber; and

FIG. 3 is a schematic, vertical sectional view of the completed storage facility for liquid natural gas made in accordance with our invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The first step in constructing our unique chamber for storing liquid gas at cryogenic temperatures is to form an enclosed space between an inner chamber and an outer chamber. The enclosed space is to contain a sufficient quantity of water so that the earth can be frozen. This space is then frozen while it is maintained in a confined condition between the inner and outer chambers and under pressure. Water, when approaching and reaching the freezing temperatures of 32 F., expands so that ice normally has a density less than water.

In our invention, the chamber or space formed between the inner and outer chambers is confined and the pressure therein is maintained at a selected level above atmospheric pressure.

The confined space prohibits the expected expansion of freezing waterand consequently, pressure in the space builds up.

After the space has been suitably frozen, the unfrozen earth is excavated interior of the frozen earth, and a roof is placed over the excavation. The roof and stressed walls and bottom form the storage chamber for the liquid gas.

Referring to the drawings, the preferred method and system will be described in detail.

In selecting a site for the formation of our improved chamber for the storage of liquid gas at cryogenic temperatures, our structure has no significant limitations as to where it can be used. Thus, the soil or earth in which the chamber is formed may be rocky, sandy, or marshy. If after selecting the site for the facility it is determined that the soil is too dry, the earth in which the chamber is to be formed is saturated with water in the areas where freezing is to occur. After making certain that sufficient water is present in the soil, structure is provided for defining an enclosed and confined space in the earth.

An outer ring of freeze pipes are driven substantially vertically into the soil. The freeze pipes 10 generally comprise a pair of concentric tubular members 12 and 14. Refrigerant is passed downwardly between the outer tubular member 12 and the inner tubular member 14 through the inlet 16. The cold refrigerant freezes the water contained in the soil around each of the freeze pipes 10. The freezing of the water occurs radially outwardly of each of the pipes 10. The circumferential spacing between each of the vertically upstanding freeze pipes 10 is to be sufficient so that a continuous substantially annular upright wall 18 of the frozen earth is formed by the outer ring of freeze pipes 10. The outside diameter of the outer frozen upright wall 18 may be any desired amount, such as 350 feet in diameter while the diametrical wall thickness is advantageously about 20-30 feet. Although reference is made herein to a circular wall, the particular shape thereof is not considered of critical importance.

A second ring of freeze pipes 20 is spaced inwardly of the outer ring of freeze pipes 10 a sufiicient distance so as to define an unfrozen space between the frozen upright wall 18 provided by the outer freeze pipes 10 and frozen upright wall 22 provided by the inner ring of freeze pipes 20. The freeze pipes 20 in the inner ring are driven to a depth less than the depth of the outer ring of freeze pipes 10 because the outer wall 18 is to be substantially deeper than the inner wall 22.

The outer freeze pipes 20 are constructed in the same manner as the outer freeze pipes 10 and include an inlet 16 for the passage of refrigerant between the outer tube 12 and the inner tube 14 and an outlet 24 extends from each freeze pipe 20 from where the spent refrigerant is passed to a refrigeration system for purposes of recooling and subsequent reuse. Although each of the freeze pipes 10 and 20 can include a separate refrigeration system for recooling the refrigerant, it is advantageous if only one set of refrigerant equipment (not shown) is used and the outlets 24 and inlets 16 of each of the freeze pipes 10 and 20 are interconnected in parallel to the equipment.

In order to provide a bottom 26 which is coextensive with the outer upright wall 18 and a bottom 28 which is coextensive with the inner upright wall 22, a plurality of freeze pipes 30, interior of the freeze pipes 10 and 20, are extended down into the soil. These freeze pipes 30 each include an outlet 24, and inlet 16, an outer tubular portion 12, and an inner tubular portion 14. The movement of the refrigerant in these freeze pipes is the same as the movement thereof in the freeze pipes 10 and 20. The freeze pipes 30 have insulation 32 positioned around the portions thereof which are exposed to soil which is not to be frozen. No insulation, however, is positioned around the freeze pipes 30 at the locations where the bottoms 26 and 28 are to be frozen. By this construction, there is substantially no heat loss from the soil to the refrigerant in the freeze pipes 30, except at those levels where there is no insulation and where the bottoms 26 and 28 are to be formed.

Upon the formation of the outer wall 18 and a contiguous frozen bottom 26 and upon the formation of the inner upright wall 22 and the contiguous bottom 28 thereof, an outer shell or chamber 34 and an inner chamber or shell 36 are provided. An unfrozen space 38 approximately 40 feet in thickness extends between the. bottom and sides of the inner shell 36 and the outer shell 34. The space 38 is defined between the outer shell 34 and the inner shell 36 is the space 38 which is frozen and ultimately acts as the structural supporting member for the underground chamber for the storage of liquefied gas at cryogenic temperatures.

The next step in our method for constructing our underground storage system comprises freezing the water contained within the space 38. Since it is an important feature of the invention to assure that the space 38 is in a confined volumetric state during the freezing thereof, the upper annular end of the space 38 must be blocked or plugged. This can be accomplished by forming a rigid plug or ring 40 at the upper end of the space 38. The ring 40 may be a concrete pad provided at a relatively shallow depth or it may be frozen to a relatively shallow depth by the use of freeze pipes (not shown). The blocking ring 40, as shown in FIG. 2, cooperates with the inner shell and outer shell 36 and 34 to define the completely confined chamber 38.

A ring of spaced freeze pipes 42 are positioned in the unfrozen earth between the upright walls 22 and 18. The freeze pipes 42 pass through the blocking ring 40. Furthermore, a plurality of internal freeze pipes 44, preferably having insulation 46 around the portions of the soil not to be frozen, extend downwardly for the purpose of freezing a floor 48 which is continuous with the upright wall 50 frozen by the freeze pipes 42.

After the freeze pipes 42 and 44 have been inserted into place, the refrigerant is passed therein through the inlet 16 to cause freezing between the walls 18 and 22 and to cause freezing between the bottoms 26 and 28 of the inner and outer shells 36 and 34.

The formation of the frozen space 38 requires careful control over the internal pressure of the space. When water reaches a temperature of about 35, it begins to expand, and when water is transformed into ice at 32, the ice expands, if not confined. Because there is a completely confined space between the frozen inner and outer shells 36 and 34 and below the upper plug 40, the cold water or ice cannot expand so internal pressures are developed. For this purpose, one or more tubes 52 having a pressure control valve 54 mounted thereon are provided. The valve 54 is preset to relieve the pressure within the confined space 38 only when the pressure in the space 38 exceeds a certain predetermined level. The stress or pressure level in the space may be varied, for example, from 0 to 2,115 killograms per square centimeter at corresponding temperatures of 0 to 22 C. The relief valve 54 bleeds water outwardly through the tube 52 if the pressure level reaches too high a level. The freezing of the space 38, while being maintained at a certain preselected pressure level or stress, continues until the space 38 has been completely frozen.

After the frozen stressed shell 56 has been formed, as seen in FIG. 3, the unfrozen soil or earth confined within the interior of the frozen shell 56 is excavated, footings or a foundation 58 is formed around the outer periphery of the upper end of the wall of the frozen shell 56, and a permanent roof 60 is provided thereover. Alternatively, the roof 60 may be constructed prior to the excavation of the interior of the frozen shell. Inlet and outlet tubes 62 and 64 pass through the roof 60 to permit the passage of liquid gas to and from the chamber 66 thus formed.

By forming walls and a floor having built in stresses, there is created a compressive stress sufficient to withstand thermal stresses created by cooling the surface of the cavity, which thermal stresses could result in cracking or widening of existing cracks of the internal surface of the cavity, thereby increasing the area for heat conduction to the stored product and also providing a potential path for leakage of the stored product. The chamber, made by our system, counteracts such thermal stresses and substantially avoids the formation of cracks or widening of existing cracks because the built in compressive stresses counteract such action.

While in the foregoing there has been provided a detailed description of a particular embodiment of the present invention, it is to be understood that all equivalents obvious to those having skill in the art are to be included within the scope of the invention as claimed.

What we claim and desire to secure by Letters Patent is:

1. A method for constructing 21 below ground chamber for the storage of liquid gas at cryogenic temperatures, said method comprising the steps of constructing an outer rigid shell, constructing an inner rigid shell spaced from said outer rigid shell, freezing the earth formation confined in the area between said outer shell and said inner shell so that said area is under a preselected built-in internal compressive stress, and excavating unfrozen earth interior of said stressed earth formation.

2. The method of claim 1 wherein pressure in said area is maintained at a predetermined level above atmospheric pressure during the said freezing step.

3. The method of claim 1 wherein said outer rigid shell is constructed by freezing the water contained in a selected portion of the earth.

4. The method of claim 1 wherein said inner rigid shell is constructed by freezing water contained in a selected portion of the earth.

5. The method of claim 4 wherein said outer rigid shell is constructed by freezing water contained in a selected portion of the earth exterior of said inner rigid shell.

6. The method of claim 1 wherein said outer rigid shell is constructed by freezing an outer shell having a bottom and sides, said inner shell is constructed by freezing an inner shell having a bottom and sides and being spaced inwardly from said outer rigid shell, and constructing a rigid portion between the space defined between the upper end of said shell sides to confine said area while freezing said area.

7. The method of claim 1 wherein a roof is added over said excavated space in order to define an enclosed chamber.

8. The method of claim 7 wherein liquid gas is added to said enclosed chamber for storing said liquid gas.

9. A method for constructing an earthen load supporting formation between inner and outer spaced and substantially concentric shells in a belowground formation, said method comprising the steps of volumetrically confining said formation between said shells, and freezing water in said earth formation, while confining said formation, at a pressure above atmospheric pressure so as to provide a built-in internal compressive stress for said load supporting formation.

10. A below ground chamber comprising an interior chamber portion, an exterior frozen shell surrounding said chamber portion, said exterior frozen shell being an earth formation having water therein at a pressure above atmospheric pressure to provide a built in internal compressive stress for said exterior frozen shell, and a top extending over said chamber to define a completely enclosed storage chamber. 

1. A method for constructing a below ground chamber for the storage of liquid gas at cryogenic temperatures, said method comprising the steps of constructing an outer rigid shell, constructing an inner rigid shell spaced from said outer rigid shell, freezing the earth formation confined in the area between said outer shell and said inner shell so that said area is under a preselected built-in internal compressive stress, and excavating unfrozen earth interior of said stressed earth formation.
 2. The method of claim 1 wherein pressure in said area is maintained at a predetermined level above atmospheric pressure during the said freezing step.
 3. The method of claim 1 wherein said outer rigid shell is constructed by freezing the water contained in a selected portion of the earth.
 4. The method of claim 1 wherein said inner rigid shell is constructed by freezing water contained in a selected portion of the earth.
 5. The method of claim 4 wherein said outer rigid shell is constructed by freezing water contained in a selected portion of the earth exterior of said inner rigid shell.
 6. The method of claim 1 wherein said outer rigid shell is constructed by freezing an outer shell having a bottom and sides, said inner shell is constructed by freezing an inner shell having a bottom and sides and being spaced inwardly from said outer rigid shell, and constructing a rigid portion between the space defined between the upper end of said shell sides to confine said area while freezing said area.
 7. The method of claim 1 wherein a roof is added over said excavated space in order to define an enclosed chamber.
 8. The method of claim 7 wherein liquid gas is added to said enclosed chamber for storing said liquid gas.
 9. A method for constructing an earthen load supporting formation between inner and outer spaced and substantially concentric shells in a belowground formation, said method coMprising the steps of volumetrically confining said formation between said shells, and freezing water in said earth formation, while confining said formation, at a pressure above atmospheric pressure so as to provide a built-in internal compressive stress for said load supporting formation.
 10. A below ground chamber comprising an interior chamber portion, an exterior frozen shell surrounding said chamber portion, said exterior frozen shell being an earth formation having water therein at a pressure above atmospheric pressure to provide a built in internal compressive stress for said exterior frozen shell, and a top extending over said chamber to define a completely enclosed storage chamber. 